1. Field of the Invention
The present invention relates to a method for monitoring the operability of a mechanical power transmission path between an actuator of an automated transmission and a shift element of the transmission.
2. Description of the Related Art
Transmissions for motor vehicles are already known in many forms. A transmission has so far mainly been understood as a manual shift transmission where, in a motor vehicle equipped with such a transmission, the driver selects the shift path and executes the shift process manually through the shift lever. Apart from those manually-actuated transmissions, automated transmissions have meanwhile also become known, where the selection and shift process of the selected gear steps occurs, for example, with control programs that operate actuators that are provided in the transmission. By the position of the shift lever, which, for example, is operated in an H-pattern, the driver of a motor vehicle having such a manual transmission system is provided with information about in which gear the transmission is engaged at that moment. If, for example, a fault occurs in the power transmission path between the shift lever and the internal actuation elements within the transmission, such as the breakage of a gear selector rod, the driver can determine that from the shift lever during the selection or shift process.
When in the case of an automated transmission the selection process of the shift path to the gear step that is to be engaged does not function, due, for example, to a fault in an actuation element of the transmission, that can lead to the previous gear remaining engaged instead of a new target gear step. To survey the selection operation and the shift operation through, for example, two electric motors in an automated transmission, movement path measurements can be obtained from those motors, but they do not enable detection of a fault in the mechanism downstream of the motors.
The present invention relates to providing a method for monitoring the operability of a mechanical power transmission path between an actuator of an automated transmission and a shift element of the transmission, so that a defect in the power transmission path can be detected before a shift process is carried out.
The invention provides a solution to that task in the independent claims. Advantageous embodiments of the method are described in the additional claims.
In accordance with the invention, a method is provided for monitoring the operability of a mechanical power transmission path between an actuator of an automated transmission and a shift element of the transmission, wherein the selection process of the gear step that is to be engaged is performed by the actuator through a control device, and wherein before a selection process a matching movement in the selection direction is carried out with the shift element until the control unit detects a reference point.
In accordance with the invention the method provides for carrying out a matching movement in the selection direction if, in general, a fault condition is encountered in such a way that a certain probability exists of a defect in the power transmission path. Such a defect can be, for example, a break in the power transmission path, which upon measurement of the movement path of the actuator cannot be detected from the actuator itself, for instance by recording the torsion angle increments of the actuator. If the fault condition is encountered, a matching movement in the direction of a selection movement is carried out by the actuator that is operated with the shift element, until the control unit detects a reference point, so that the probability for the defect can be negated.
Therefore, the invention provides that the reference point is a stop at which the shift element stops in the selection direction, and that the stop is detected by the control unit. The stop can be a stop within the transmission, for example in the neutral path of the transmission. When the shift element meets with the stop, the control unit detects that the stop is encountered, wherein for that purpose, for example, the rotational speed of the actuator can be monitored for the selection process so that a drastic reduction in the rotational speed of the actuator indicates that it has reached the stop. Additionally, an increase in the voltage and/or the current for controlling the actuator can be monitored.
Based on an advantageous embodiment in accordance with the invention, the control unit monitors the sum of the kinetic energy of the actuator and the electric energy fed to the actuator, and compares it with a reference value of elastic energy that can be absorbed by the power transmission path, and carries out the alignment movement after the reference value has been exceeded.
When the actuator in the form of an electric motor is supplied with current, the rotor shaft of the electric motor is accelerated so that it has a certain kinetic energy. After current flow to the electric motor ceases, the motor causes a force to be introduced into the power transmission path, in, for example, a mechanism downstream of the electric motor, with which the force is transmitted to the shift element that is in the form of, for example, a shift finger. When the shift element in the transmission rests against a stop, continued running of the electric motor leads to a winding up or tensioning of the mechanism downstream of the electric motor. A monitoring of the sum of the kinetic energy of the actuator and the electrical energy fed to the actuator enables a determination as to whether that sum exceeds a reference value or threshold value, and that still can be absorbed within the framework of an elastic deformation of the mechanism that is downstream of the electric motor without being damaged.
Once that sum reaches the reference value, the method in accordance with the invention provides for a alignment movement, which leads to the determination of whether the mechanism that is downstream of the electric motor is still functional, which can be recognized by the control unit by the fact that the shift element actuated by the mechanism has reached a stop whose reference position is known, or whether that is not the case.
Since the reference value is not set so high that the mechanism downstream of the electric motor incurs permanent damage, the fact that this reference value has been reached does not lead to such damage. In accordance with the method, there is also provided a proceeding when the above-described sum not only reaches the reference value, but substantially exceeds it. Upon exceeding the reference value beyond a previously established threshold value, the control unit can issue an error message and indicate that to the driver of the motor vehicle with the automated transmission.
Due to the fact that the motor vehicle with the automated transmission is exposed to varying temperature conditions, which can be substantially influenced by, for example, an internal combustion engine that is coupled with the transmission, the invention also provides for a feature based on which the reference value is determined as a function of the temperature in the region of the power transmission path.
An increase in the measured temperature can therefore lead, for example, to a lowering of the reference value, since the mechanism that is downstream of the electric motor is exposed to higher temperature stress, and, thus, the energy that can be absorbed within the framework of elastic deformation without a permanent deformation is reduced.
Since the power transmission path in the form of a mechanism that is downstream of an electric motor must experience less mechanical stress at elevated temperatures, the method in accordance with the invention provides that the electrical energy that is fed to the actuator is limited as a function of the kinetic energy of the actuator and the temperature in the region of the power transmission path.
Finally, the invention also provides that the electrical energy that is fed to the actuator is reduced after detecting a stop, so that the control voltage applied to the actuator, or the load current fed to the actuator, is clearly reduced after the control unit detects the stop.
The control unit can continuously calculate the above-mentioned sum of kinetic energy and electrical energy. The electrical energy can be limited as a function of the kinetic energy and, for example, the temperature can be limited to a maximally permissible value. During a selection process, the highest motor rotational speed value that is associated with the highest kinetic energy of the rotor shaft is taken into consideration, and the electrical energy is limited in relation to it.
Test series can help determine which energy sum can be introduced into the selection mechanism for a permissible elastic deformation of the selection mechanism, which can also occur as a function of the temperature in the region of the selection mechanism. When that energy sum has been reached, there exists a certain probability for a defect in the selection mechanism. With a reference movement or a alignment movement for the purpose of detecting a stop in the selection direction, one can determine whether or not a defect exists. The degree of confidence in the result can be increased through repetition. If the energy sum should clearly exceed the reference value, the possibility of lasting damage is higher, and it can be provided that the control unit gives corresponding error information to the driver of the motor vehicle, in addition to bringing about a reference movement, or as an alternative to a reference movement.
Based on the invention, a method is also provided for monitoring the operability of a mechanical power transmission path between an actuator of an automated transmission and a shift element of the transmission, wherein the selection process for the gear step that is to be engaged is performed with the actuator through a control unit, wherein the threshold force that leads to a permissible elastic deformation of the power transmission path is established, and wherein before or upon reaching the threshold force an overload clutch that is provided in the power transmission path is opened.
An overload clutch can be provided in the power transmission path between the actuator and the automated transmission, which disengages upon reaching a certain load threshold and thereby interrupts the power flow between the actuator and the shift element. Damage to the power transmission path is thereby prevented.
After the overload clutch has been disengaged in order to prevent damage, it can be engaged again, whereupon a alignment movement in the selection direction is performed with the shift element before a selection process, until the control unit detects a reference point. This start to the reference point is used on the one hand to determine that the mechanism downstream of the actuator was not damaged, and on the other hand to also perform a referencing process of the torsion angle increment sensors of the actuator. This also clarifies that the engagement of the overload clutch does not have to occur at a true angle or a true path. Upon engagement of the overload clutch, it acts like a positive-locking connection.
In test series, the energy that the mechanism that is arranged after the actuator requires to actuate the shift element of the transmission within the framework of elastic deformation without lasting damage can be determined. That energy can also be determined as a function of the temperature in the region of the power transmission path. The power peak occurring upon reaching the respective energy is determined, and the overload clutch is designed in such a way that it disengages at a power threshold below the tolerable power poak. When the sum of the kinetic energy of the actuator and the electrical energy fed to the actuator exceeds the disengagement threshold of the overload clutch, the overload clutch disengages and in that way avoids damage to the power train.
Upon engagement of the overload clutch, an appropriate referencing process is performed, such as the one described above. By reaching a stop in the transmission, a positive determination is made that the power transmission string was not damaged, and thereby the torsion angle increment measurement can also be adjusted.
The invented method is provided in particular for utilization as a shift safety device against a shift between the forward motion direction and the reverse motion direction of the automated transmission.